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New Zealand is starting to get back to normal today after the Antarctic blast which brought the first snow in decades to much of the country, but there is still danger on the roads, with black ice expected in many areas over the coming days.

This week's cold snap has closed roads, airports and schools, and left hundreds without power.

All North Island state highways were open after the Desert Road reopened this morning followed by the Rimutaka Hill road between Wellington and the Wairarapa this afternoon.

The Lewis, Arthurs and Porter mountain passes remain closed in the South Island.

Queenstown, Dunedin, Christchurch and Wellington airports were all open and most schools were expected to reopen tomorrow.

Bluebridge and Interislander ferry passenger services would resume normal sailing times tomorrow, after both cancelled sailings today due to swells in the Cook Strait.

WeatherWatch.co.nz head analyst Philip Duncan said the wintry blast was starting to ease but snow flurries were still hitting parts of Canterbury and the wettest and coldest parts were in the North Island's east coast.

The freezing level was rising, so snow would fall only in higher country.

However, tomorrow morning would be extremely cold and minus 10degC was possible in the Central Otago basin.

"Many areas are still facing bitterly cold winds, sleet rain and even snow to sea level - but many others are seeing the sun.''

Mr Duncan says frosty conditions will stretch from Southland to Northland with severe frosts in the south and light to heavy frosts in the north.

"With so much snow melt and wet roads there is an extremely high risk of black ice on Thursday morning - and that risk will become more and more widespread over the next few days as this high slowly pushes in".

Frosty conditions may also affect parts of Canterbury dispite a few lingering snow and rain showers - but they will become isolated.

Frosts are less likely on the North Island's east coast from Wellington to Gisborne due to frequent showers and brisk winds. Severe frosts are expected across the central North Island too, in sheltered areas away from the brisk southerly wind.

Heavy to severe frosts are also expected from inland Taranaki to King Country and Waikato.

Mr Duncan said the centre of the low pressure weather system was now 2500km southeast of Christchurch and moving away from New Zealand.

"The main event has well and truly passed now, but we're still being affected by the tail end, so more heavy snow down to a few hundred metres from Canterbury to Hawke's Bay and wintry, sleety, conditions to sea level.''

St John regional operations manager for the South Island Chris Haines said the ambulance service was operating at usual levels today.

Christchurch lines company Orion this morning said power was out for 60 customers in Christchurch and central Canterbury - about 40 in parts of rural Leeston, Tai Tapu and Dunsandel, and fewer than 20 individual customers in the city.

North Island lines company Powerco said high winds and snow caused trees and branches to tear down overhead lines, cutting power to more than 37,000 customers since Sunday.

Supply was cut to about 500 customers in Hunterville and Tararua overnight due to the severe weather, and a further 4200 in Wanganui this morning. A car which crashed into a power pole in Wanganui cut power to 10 properties last night.

There were currently about 250 properties without supply spread across Manawatu, Taranaki and Wanganui. The majority of affected customers were expected to have supply restored by the end of today, although a small number may be without power where access was difficult or damage extensive.